modify code generation to reduce whitespace

[gvwilson]

@alexcjohnson wrote:

• We should be able to reduce the whitespace significantly, to make the file smaller. Could even collapse it to a single line, I'm not sure there's much value keeping it human-readable, but maybe @emilykl has opinions about this. If we really want to optimize file size we could also change its structure a bit - like if every entry is a dict {params, superclass} this could be converted to a length-2 list. But the whitespace is the biggest piece of this.
• json.load is pretty fast, ~41ms on my computer. But it's even faster if we just make this a Python file. In my quick test I just added:

true=True
false=False
null=None
v = 

to the beginning of the file to convert the JSON to Python, and then from validators._validators import v took only ~25ms. (If we do this for real we should be able to tweak the json.dump to output Python in the first place so we don't need to alias true, false, and null).